1. Field of the Invention
The invention relates to a process for preparing carbonic acid esters having a quaternary group which esters are useful as bleach precursors in detergent compositions.
2. The Prior Art
Detergent compositions that rely upon sodium perborate as a bleach normally require a precursor to activate the oxygen-releasing compound where wash-water temperatures are below 60.degree. C. A recently issued patent, U.S. Pat. No. 4,751,015 (Humphreys et al.), reported an exceptionally effective bleach precursor family of compounds identified as quaternary ammonium or phosphonium substituted carbonic acid esters. These precursors were reported synthesized in a two-step procedure. For instance, 2-(N,N,N-trimethylammonium)ethyl sodium 4-sulphophenyl carbonate chloride (SPCC) was synthesized by first preparing choline chloroformate chloride through reaction of phosgene with choline chloride in a chloroform solution. The choline chloroformate chloride was then isolated as a crystalline solid. In a second step, the solid choline chloroformate chloride was added to an aqueous solution of sodium 4-phenol sulfonate whose phenolic proton was removed with an equimolar amount sodium hydroxide.
A number of problems are associated with this process. For instance, there are handling problems with choline chloroformate chloride, a highly hygroscopic material Spontaneous crystallization of the chloroformate from solution has been noted. This presents a challenge in commercial production to avoid pipeline constriction. Furthermore, yields of the final product, SPCC, are variable, sometimes being even quite poor (40-85%). Instability of the final product is a still further problem.
Consequently, it is an object of the present invention to provide an improved process for the synthesis of quaternary ammonium or phosphonium substituted carbonic acid esters.
A more specific object of the present invention is to provide an improved process for obtaining the aforementioned carbonic acid esters which does not necessitate isolation of the intermediate chloroformate chlorides.
A further object of the present invention is to provide a synthesis of carbonic acid esters that results in a high and relatively reproducible product yield.
A still further object of the present invention is to provide a synthesis of carbonic acid esters such that these esters remain stable under reaction conditions.